Quicktime File Format (2012-08-14).pdf

Movie AtomsTrack AtomsCompressed matte atomThe actual matte data.See “Compressed Matte Atoms” (page 69) for details.Compressed Matte AtomsThe compressed matte atom specifies the image description structure and the matte data associated with aparticular matte atom. Compressed matte atoms have an atom type value of 'kmat'.The layout of the compressed matte atom is shown in Figure 2-14 (page 68).Compressed matte atoms contain the following data elements.SizeA 32-bit integer that specifies the number of bytes in this compressed matte atom.TypeA 32-bit integer that identifies the atom type; this field must be set to 'kmat'.VersionA 1-byte specification of the version of this compressed matte atom.FlagsThree bytes of space for flags. Set this field to 0.Matte image description structureAn image description structure associated with this matte data. The image description contains detailedinformation that governs how the matte data is used. See “Video Sample Description” (page 155) for moreinformation about image descriptions.Matte dataThe compressed matte data, which is of variable length.Edit AtomsYou use edit atoms to define the portions of the media that are to be used to build up a track for a movie. Theedits themselves are contained in an edit list table, which consists of time offset and duration values for eachsegment. Edit atoms have an atom type value of 'edts'.Figure 2-15 (page 70) shows the layout of an edit atom.In the absence of an edit list, the presentation of a track starts immediately. An empty edit is used to offsetthe start time of a track.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.69